A plasma processing apparatus generates plasma in a process chamber. A workpiece supported by a platen is positioned in the process chamber. The plasma processing apparatus may include, but not be limited to, doping systems, etching systems, and deposition systems. One drawback with a conventional plasma processing apparatus is cross contamination if one input process gas is changed to a different input process gas. This is due to deposits that form on the interior surfaces of the process chamber housing that may contaminate the later process. For example, a plasma doping apparatus may receive a p-type process gas such as BF3 and boron deposits may build up over time on interior surfaces and components. If it is desired to change the BF3 process gas to an n-type process gas such as PH3, the boron deposits would likely contribute to cross contamination problems if not cleaned properly. Accordingly, a conventional cleaning process may be run to clean the interior surfaces of the process chamber.
A conventional cleaning process may input a fluorine containing gas directly input to the process chamber or may use a remote plasma generator to generate many fluorine radicals. In either instance, the cleaning takes place via a chemical reaction within the process chamber. One drawback with this conventional cleaning process is that it requires a flow rate as high as 500-2,000 standard cubic centimeters per minute (SCCM) for the cleaning gas. Another drawback is that the process chamber is operated at high pressure as high as several hundred mTorr to several Torr during the cleaning process. Reaching this high pressure takes time as some pumps such as a turbo molecular pump may be shut down and alternative mechanical pumps are employed to maintain the high pressure during the cleaning process. The chemical reaction at the high pressure and flow rate may be so aggressive that it damages the interior surfaces of the process chamber housing and components in the process chamber such as a shield ring that may surround the platen. Yet another drawback is that this makes it inefficient to switch between different process gases in the same process chamber.
Accordingly, there is a need for a plasma processing apparatus and a method which overcomes the above described inadequacies and shortcomings.